Thermal-hydraulic characterization of high heat flux components for fusion reactors
Some components of fusion reactors are estimated to be subjected to very high heat fluxes, such as about 20 MW/m2, i.e., an order of magnitude higher than those encountered in the thermal hydraulic design of the light water reactor core (typically 1 MW/m2). This called for a heavy experimental research conducted in many research centers, which permitted to verify the possibility of removing such a high heat flux using water at high velocity (10-15 m/s) and high subcooling (200 K).
To obtain accurate and precise design tools for the thermal hydraulic design of high heat flux components in fusion reactors, a full understanding of thermal crisis mechanisms under such extreme thermal hydraulic conditions must be accomplished.
In spite of the large number of available data points, many of which carried out at the ITFD, a complete knowledge of the phenomenon has not yet been reached. We are currently testing a visualized test section using ultra-high speed micro-cinematography, to get local information about the leading mechanisms for the critical heat flux under these conditions. Very small size of the bubbles (few tens of microns) and the high velocity of the liquid (up to 10 m/s) make the cinematography very critical, and the use of a pulsed laser is pursued.
A further experiment on an ENEA patent to remove high heat fluxes, named High Efficiency Thermal Shield, HETS, is underway. It uses jet impingement and continuous flow direction change to reach high heat flux removal. The experimental programme is carried out on the STAF facility.